Cloud point extraction, preconcentration and spectrophotometric determination of erbium(III)-2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminophenol

The extraction and preconcentration of metal chelates via surfactant-mediated phase separation was studied. The effects on extraction parameters of several experimental variables were evaluated. A successive approximation method, using a least-squares computer program, was employed for the calculation of partition and acid dissociation constants of the chelating reagent. A new, high-sensitive and low-cost methodology for the determination of Er(III)-2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminophenol — with the nonionic surfactant, polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5), with a cloud point extraction step prior to absorptiometric determination — was developed and optimized. Under the optimal experimental conditions, the molar absorptivity was 1.27 × 105 1 mol−1cm−1. Calibration plot of absorbance (584 nm) vs. concentration was linear within the range 0.02–2 mg l−1 Er(III). The lower limit of detection (LOD) was 1.48 × 10−7 mol l−1. The proposed procedure was successfully applied to the determination of Er(III) in synthetic samples, reproducing superconducting materials and permanent magnets.